1. Field of the invention
The present invention concerns control buttons that must be depressed to operate an underlying component of any kind, for example an electrical component of any kind.
2. Description of the prior art
Usually called "mushroom head pushbuttons" when their shape is such that they can be actuated with the palm of the hand, these control buttons usually include a guide body by means of which they can be mounted on any kind of support, a plunger to actuate the underlying component axially mobile in the guide body in the manner of a piston, a control member in the general shape of a mushroom axially mobile in the guide body between an "out" inactive position and an "in" active position and having a head to be actuated by the user and a shank to actuate the plunger, and, associated with said control member, return spring means which urge it at all times towards its "out" inactive position.
The present invention is more particularly concerned with control buttons known as "push-pull type latching" control buttons which further include latching means on the path of movement of the plunger adapted to retain the latter releasably in at least one axial direction, namely the axial direction from the "in" active position to the "out" inactive position of the control member and, operative between the plunger and the shank of the control member, lost motion coupling means enabling the control member to apply traction to the plunger to return the control member to its "out" inactive position.
One example of the use of these control buttons is to stop plant quickly and permanently in an emergency.
To stop the plant all that is required is to depress the control member.
This moves the plunger towards the component in order to actuate it, for example to switch it from a first state to another state.
At the same time, the plunger catches under the latching means and, retained by the latter, it retains the control member in the "in" active position which holds the underlying component in its new state.
To return this component to its initial state, i.e. to bring about the reverse switching of this component from one state to the other, sufficient traction must be applied to the control member for the plunger, entrained by the control member, to overcome the resistance of the latching means and move in the opposite axial direction and thereby release the component.
In practise, however, given the travels available, the plunger actuates the underlying component before it passes the latching means.
In other words, this component is switched from one state to the other before the plunger and therefore the control member are latched.
Consequently, if the control member is released before latching takes place, the underlying component inevitably returns to its initial state, after being temporarily switched to another state.
In other words, the underlying component unintentionally changes state twice in succession.
A general object of the present invention is an arrangement avoiding this drawback.